draw

@screen @ctrl

screen:
  CLS
  LIT 0 LIT 10 PSH PSH do: RSI LIT 40 SFT
    LIT 0 LIT f PSH PSH while:
      DUP RSI ADD OVR RSI ADD LDB SET
      PUL INC PSH
      RSI RSJ NEQ LIT @while JCN
      PUL PUL POP POP POP
    PUL INC PSH
    RSI RSJ NEQ LIT @do JCN 
    PUL PUL POP POP
  LIT pos: 0 FRM LIT a MOD LIT 9 LTH SET
BRK

ctrl:
  KEY LIT 1  AND LIT @up    JCR
  KEY LIT 2  AND LIT @down  JCR
  KEY LIT 4  AND LIT @left  JCR
  KEY LIT 8  AND LIT @right JCR
  KEY LIT 10 AND LIT @keya  JCR
  KEY LIT 20 AND LIT @keyb  JCR
BRK

up:    LIT @pos LDA LIT 10 SUB LIT @pos STA RET
down:  LIT @pos LDA LIT 10 ADD LIT @pos STA RET
left:  LIT @pos LDA DEC LIT @pos STA RET
right: LIT @pos LDA INC LIT @pos STA RET
keya:  LIT 1 LIT @pos LDA STB RET
keyb:  LIT 0 LIT @pos LDA STB RET